Pazopanib is a tyrosine kinase inhibitor of Formula Ia.

Pazopanib is marketed as the hydrochloride salt, with the chemical name 5-[[4-[(2,3-dimethyl-2H-indazol-6-yl)methylamino]-2-pyrimidinyl]amino]-2-methylbenzenesulfonamide monohydrochloride, having the structure as depicted in Formula I:

U.S. Pat. No. 7,105,530 provides a process for the preparation of a hydrochloride salt of a compound of Formula II
involving the reduction of 2,3-dimethyl-6-nitro-2H-indazole with tin (II) chloride in concentrated hydrochloric acid in the presence of 2-methoxyethyl ether at 0° C. It also describes the preparation of a compound of Formula III
involving the reaction of a hydrochloride salt of compound of Formula II with 2,4-dichloropyrimidine in the presence of a base and solvent mixture of tetrahydrofuran/ethanol followed by stirring for 4 hours at 85° C.
PCT Publication No. WO 2007/064752 provides a process for the preparation of a compound of Formula II comprising reducing 2,3-dimethyl-6-nitro-2H-indazole with 10% Palladium-carbon (50% wet) in the presence of methanol, followed by the addition of ammonium formate at a rate that ensures the reaction temperature is maintained at or between 25° C. and 30° C. It also discloses the preparation of a compound of Formula III comprising heating the compound of Formula II with sodium bicarbonate in presence of tetrahydrofuran and ethanol at or between 75° C. and 80° C. followed by cooling to 20° C. to 25° C.
The present invention provides a process for the preparation of a compound of Formula II which offers recycling of the Raney nickel catalyst used in the process, and an easy filtration work-up procedure. Further, the present invention offers selective reduction under mild conditions that is economical to use at an industrial scale.
The present invention also provides a process for the preparation of compound of Formula III which avoids the use of two or more solvents, and additionally, also circumvents heating and cooling procedures during the reaction. The aforesaid advantages yield a compound of Formula III with a lesser amount of N-(4-chloropyrimidin-2-yl)-2,3-dimethyl-2H-indazol-6-amine (CPDMI) impurity.
The compounds of Formula II and Formula III prepared by the present invention yield a compound of Formula Ia or its salts in comparable yield and suitable purity required for medicinal preparations.